Yersinia pestis is the causative agent of plague and constitutes an important biowarfare and bioterror agent. Aerosolized Yersinia pestis, the likely form of delivery by terrorists, causes pneumonic plague, a disease feared for its high mortality rate and ability to be transmitted from person-to-person. Fortunately, previous studies identified two key protective antigens against plague, the F1 capsular antigen and LcrV, also known as the V-antigen. Our goal is to develop attenuated bacterial vaccine vectors to deliver these protective antigens. Live bacterial vectors represent an important contribution to vaccine technology in that they offer the possibility of mucosal immunity, rapid delivery and a high degree of safety. For these reasons, live bacterial vaccines should be part of our armamentarium against biowarfare agents such as Yersinia pestis. The particular emphasis of this proposal is to develop enteric vaccines as mucosal priming agents that can be used in conjuction with parenteral subunit vaccines, such that the response to the latter is faster, more balanced and more vigorous than in the absence of this mucosal priming. The products to be produced under this proposal are: 1) Y. pestis caf1 operon (expressing F1) and IcrG/IcrV hybrid (expressing V antigen) expressed in Salmonella Typhi CVD908-htrA; 2) co-expression of the caf1 operon and yopE-IcrV to yield secreted LcrV; 3) a Yersinia pseuotuberculosis yopK mutant strain expressing caf1 operon with surface localized F1 and secreted LcrV; 4) Yersinia pestis guaBA mutant expressing surface-localized F1 and secreted LcrV. During and at the conclusion of the funding period, several products will be ready for Phase 1 human testing, most likely in conjunction with subunit vaccines already in advanced stages of development.